In the manufacture of semiconductor devices, various processing apparatuses (semiconductor manufacturing apparatuses) are employed for performing various processes such as oxidation processes, diffusion processes, and CVD (Chemical Vapor Deposition) processes, to objects to be processed such as semiconductor wafers (also referred to as “wafer” below). One of the known processing apparatuses is a heat processing apparatus of a batch type, such as a vertical-type heat processing apparatus, which is capable of simultaneously heat-processing a number of objects to be processed.
The vertical-type heat processing apparatus includes: a heat processing furnace; a holder (also referred to as “boat”) capable of being carried into the heat processing furnace and carried out therefrom, with holding therein a number of objects to be processed at predetermined vertical intervals therebetween in a tier-like manner; and a transfer mechanism including a base table capable of vertically moving and rotating, and a substrate supporter capable of horizontally moving on the base table. The transfer mechanism transfers an object to be processed (e.g., wafer) between a container containing a plurality of objects to be processed at predetermined intervals therebetween, and the holder (see, JP2001-223254A). The transfer mechanism is an automatic transfer robot for accomplishing a predetermined, transfer operation based on a program preset in a controller.
During the transfer operation of wafers, some abnormal circumstances may occur, that is, there is a possibility that the wafer in the boat falls off a groove (one side of the wafer is disengaged from the groove of the boat), breaks, or protrudes from the boat. In such a case, the transfer mechanism driven under a normal sequence control may interfere (collide) with the abnormal wafer and knock the boat over, resulting in damage of the wafers and the boat.